1. Field of the Invention
The present invention relates generally to blood handling equipment and more particularly to a blood reservoir and filter device wherein blood removed from the human body during surgical procedures can be filtered and temporarily stored before being further treated and returned to the patient.
2. Description of the Prior Art
In recent years, it has become more desirable and possible to recapture and treat blood that was previously lost during surgical procedures. The advent of equipment for this purpose has taken on new significance due to the risks inherent in normal blood transfusions which were previously necessary to replace blood that was lost or discarded during surgery. The risks of blood transfusions obviously include the exposure to A.I.D.S. and other such diseases which may be carried by the blood of a third-party source of the blood.
Blood removed from a surgical wound is usually withdrawn with a suitable vacuum source, but since the blood is typically contaminated with gas bubbles, tissues fragments, surgical debris and the like, it is necessary to filter and treat the blood before it is returned to the surgical patient. It is also desirable that the blood, while outside the human body, be carefully handled so as not to traumatize and/or otherwise damage the blood before its reinfusion into the patient.
Blood can be damaged through trauma if it is allowed to abruptly impact hard surfaces, and for this reason, filter devices for receiving such blood have been very carefully designed. For example, U.S. Pat. No. 4,737,139 issued to Zupkas et al. shows that it is desirable to allow incoming blood to flow smoothly over an entry cone having a rounded upper tip so that the blood does not fall a significant distance onto a hard surface where it might be damaged. It is also known, as evidenced by the patents to Raible Nos. 4,157,965 and 4,164,468, to allow the blood to flow smoothly over a conical surface as it passes through a filter medium again to minimize the exposure to trauma. A problem with filter devices of the type disclosed in the Raible patents, however, resides in the fact that, after the blood has passed through the filter and flowed smoothly across a conical surface, it is allowed to pass through notches in the surface from where the blood falls onto a hard bottom wall of the device. The Raible devices minimize the trauma by reducing the distance through which the blood falls onto the hard surface at the bottom of the device, but this arrangement necessitates a small receiving and storing area beneath the filter medium.
Since blood sometimes needs to be retained in a filter device until it can be further processed for reinfusion, it is desirable that the holding space within the filter device be of a sufficient size to retain the filtered blood in non-engagement with the filter medium. This is important due to the fact that typically the filter medium is treated with a silicone material to facilitate defoaming of the blood and prolonged exposure to the silicone material can contaminate the blood. As will be appreciated, if the storage space within the filter device is enlarged to accommodate a significant volume of blood in non-contact with the filter medium, devices of the type disclosed in the Raible patents, wherein the blood is allowed to drop from a conical surface to the bottom of the filter, become undesirable as the distance the blood falls is enlarged thereby exposing it to trauma.
U.S. Pat. No. 4,664,682 issued to Monzen discloses a blood filter device which deals with this particular problem by elevating the filter material within an outer housing and allowing the blood to flow downwardly from the filter medium along an inverted conical surface toward the bottom of the housing where the blood flow is transferred to a second upright conical surface before being removed from the housing. In other words, by transferring the blood between cooperating conical surfaces, the device enables the blood to pass through a relatively large storage area without allowing the blood to fall a great distance into contact with a hard surface where it might be traumatized.
Another problem with most prior art filters is that the filter medium, which is typically cylindrical in configuration to define an enclosed chamber into which blood is introduced, is suspended or otherwise secured to the outside of a supporting filter cage. The cage is made of a hard material so that blood that is allowed to engage the cage, including a hard bottom wall thereof, can be traumatized unless it is carefully handled by passage across conical dispersion surfaces such as of the type found in the previously mentioned patent to Zupkas et al.
The provision of such conical flow plates of the type found in the Monzen patent, add expense and complexity to the filters and therefore are not entirely satisfactory for that reason. Without the conical flow plates, however, the blood can be easily damaged by impact with relatively hard surfaces within the device.
U.S. Pat. No. 4,243,531 issued to Crockett et al. deals with the cage problem by providing a solid mass of filter material on the inside of a perforated cage so that the blood engages the filter immediately upon entry into the device and therefore does not fall directly upon the relatively hard cage material. After passing through the filter medium and subsequently the perforated wall of the cage, however, the blood must flow along the relatively rough outer surface of the cage where it continuously encounters and engages the walls of the numerous perforations in the cage. This engagement, of course, again exposes the blood to possible trauma which it is desirable to avoid.
It will be appreciated from the afore-noted description of the prior art that, while the industry is aware of the problems which are desirable to avoid when treating and handling blood in a reservoir and filtering device, there are shortcomings in each of the prior art devices which negatively impact the device either from an operation or economic standpoint. It is to overcome these shortcomings in the prior art that the present invention has been developed.